Don't show unknown source dlg if they were allowed

Once the unknown sources have been temproary allowed, never show the
dialog and always continue to install. Preserve this information over a
destroy->create.

I also converted the dialogs to a non-deprecated interface.

Test: entered unknown sources dialog, entered mutli-window-mode,
      returned to app. (Workflow from b/34314562)
Change-Id: I7c7a407bddaa868cb917827eed3389c334126222